I was watching “The Dam Busters” last week-end with the pictures of those fabulous Lancasters, and a question started nagging at me. Most, if not all, of the U.S. medium and heavy bombers used radial engines, but the RAF, and the Luftwaffe, used more in-line engines. Why?
I figure some of you aero heads would have a logical answer.
Thanks,
Carl
Radials were air cooled thus no need to carry radiators that could be punctured. Radials could take a lot of damage and still keep on running. The drawback was they had large frontal area and increased drag. They were also easier to service. Both engines have their pros and cons. Another thought to consider is production capacity. We here in the US had unlimited capacity to produce bombers as compared to others on either side. Build them simple and fast…they were expendable resources. Overwhelm the enemy with volume!
I believe that the US Navy preferred radial engined aircraft for these very reasons, and in addition it obviated the need for shipboard storage tanks of coolant.
When you look at RAF aircraft, particularly the “big four” of the best known types (eg. Spitfire, Hurricane, Moaquito, Lancaster) one could be forgiven for thinking that the Merlin was the only aero engine the Brits produced. Stray a little off the familiar path and you will find many radial engined types (primarily bombers).
Bristol Blenheim
Bristol Beaufort
Bristol Beaufighter
Handley Page Hampden
Handley Page Halifax (though a small number were built with Merlins)
Vickers Wellington
Hawker Fury/Sea Fury
Short Stirling
Short Sunderland
I’m sure there’s more [:)]
They also have more horsepower and cubic inches.
I wish my dad was still around so I could give you a radial engine mechanic’s perspective.
My dad worked on a lot of them after the Marine Corps here at the Alameda Naval Air Station.
I bet it would be a bear to change the plugs on a Radial engine.I bet the mechs had to have a system to tell which plugs were changed and which were not!
In the late '30’s, European aero engineers considered the inline engine as the leading technology for aircraft due to low drag, high power output and potential for future development. Germany basically shunned the radial except where performance was not critical, such as second line bombers. In America and Japan generally the radial engine was supreme, because American aero engine designers had developed some very good radial engine designs that were powerful, low weight and reliable. Note that most radial engine designs in the rest of the world were originally license built variants of either Pratt & Whitney or Wright. The only significant American inline design was the Allison and it was plagued with problems, limiting its effective use to lower altitudes.
It turned out the radial engine had the better potential in the long run, simply because as engines gained more power, cooling them became a bigger problem. With liquid cooled designs that means more weight in the radiators and coolant tanks, requiring more power, etc. Radials offered the better power/weight ratio and it’s why most aircraft after the war were radial powered. Consider airliners.
All types of engines were produced in very great numbers during the war, and after the war it simply made sense to continue to use them in applications where it made sense. The Brits had many Merlins on hand from the war so continued to install them in designs post-war. Jet engines eventually surpassed both inline and radial designs.
My 2 cents, anyway.
Tim
One round motor that didn’t have nearly the drag problem of others was the P&W -2800… Because it’s cooling fin design allowed it to get rid rid of great gobs of heat very quickly, the aircraft with that engine installed (like the Corsair, Black Widow, Marauder, Thunderbolt & three outta four of the prop-driven Grumman Cats to name a few) could be very “close-cowled” to reduce the drag… (And there’s only 36 plugs to change, Philo…[:D])
Damliar-Benz tended to produce In-line engines, but BMW tended to produce radial engines. One of the reasons Kurt Tank got the FW-190 project approved was becuase it would be powered by a BMW radial engine. He argued that Daimlar-Benz would not be able to supply enough engines to meet demand.
I’m not a Luft expert, but the radial engine was a big player. Remember that alot of them were license built from Wright or from Pratt, so that the technology flow was cut off at a certain point. The RAF used all manner of Bristol radial engines in all kinds of a/c, Beaufighters, on and on.
The Us did not use inline engines in bombers as all of that production was sent to Warhawks and later, to Mustangs. I do not see an inherent bias one way or the other, rather what was available and many an airframe flew both, see FW190/TA152.
But nowadays there are only a few types that use radial engines. In general aviation the inline (often boxer) engine is preffered. Why is that?
I’m guessing because there’s no big piston aero engines in use any more. Anything over a couple of hundred horsepower is a turboprop or a jet. Smaller piston engines don’t see the advantages of being a radial. There are a couple of small radials, one’s made in Australia. Jesse James put one of them in a motorcycle a couple of years ago.
a boxer is sort of a two bank or three bank radial with only two cylinders per bank, right?[;)]
http://thekneeslider.com/archives/2006/05/10/radial-engine-powered-motorcycle/
Modern horizontally-opposed aircraft engines offer far less frontal area than radials, don’t leak oil everywhere, are more fuel-efficient, are more maintenance-friendly, and fit into a much smaller, more streamlined package. A radial is great when you need a whopping huge power-to-weight ratio, but most general aviation aircraft simply aren’t in need of that kind of power. Designers of small aircraft are more interested in reducing drag than increasing power - a more powerful engine usually comes with a hefty penalty in terms of weight. A powerful plane that can’t carry any people or stuff isn’t much use in the general aviation world.
The “boxer” configuration is also preferred to an inline one, again because of drag considerations. To streamline an inline engine, you need a tall skinny airframe. Most general aviation types use side-by-side rather than tandem seating, so you don’t really want that shape. You want a wide, low shape instead.
These days, turbines are the way to go if you need serious lifting capability in a small aircraft. The Pratt & Whitney PT-6A, for example, (by far the most popular turbine in service) is thermodynamically capable of making roughly 1,600 shaft horsepower. In most installations its downgraded to anywhere from 500 to 1,200 hp, still a very high power to weight ratio. It’s lightweight, famously reliable… and a lot cheaper to run and maintain than a radial. There are an awful lot of radial types in use that have been converted to turbines: DHC Beavers and Otters are a prime example, also S-2 Trackers used for wildfire fighting.
Kevin
radial engines are virtually unrepairable in the field; unless it’s something externally mounted on the engine. Where as an inline engine can be opened up to a certain extent (say to replace a valve spring or even go so far as change the camshaft. This is why you will see pics of them constantly swapping out radial engines. But on the otherhand a radial engine requires less tooling to build it, and in theory the main bearing system should last the life of the casting except for one major flaw in the design concept. Where as an inline engine tends to load the main bearing system in one constant direction. The idea that an inline engine is not as reliable as a radial is bunk. I’ve seen pictures of Mustang engines with holes in the side of the block big enough to put both of your hand thru. The real problem with radial engines is fuel usage and oil leakage. You must run a very dense charge to also help cool the engine, but on the otherhand when you do this you also must take the chance on fouling the spark plugs. Radial do tend to produce more horse power, but this only because of their very large displacement (also greatly contributing to fuel usage). Where a typical inline engine will run a much leaner charge, and make similar horse power in a much smaller displacement engine. Inline engines are typically water cooled (but not always), and have a much narrower cross section as has been noted. Also tend to cool better at high altitudes than air cooled engines (this is really almost a mute point as it’s much colder at high altitudes). Inlines do require a radiator, but on the otherhand a radial requires an external oil tank (there is no real way to cast a wet sump crank case in them).
When it comes to manufacturing these two engines you will find that you need less space with the radial, and the main assemblies (crank case and cylinders and heads) can be done with less equipment. But on the otherhand an inline renders itself to the use of a transfer machining setup similar to the way they machine automobiles blocks and heads these days. What this means is the every time the machine cycles (about every four or five minutes) you spit out a finished cylinder block. That’s about 100 blocks a shift or as much as three hundred a day. You’ll be hard pressed to do that in two and a half days building radial engines! Also radials are so complicated that the assembly takes well over twice the time (in the end you will have several times the man hours in a radial than you will in an inline)
To take this further: during WWII the war department actually built some B17’s and B29’s with inline engines to see if the concept would work. They found the water cooled inline engines out performed the radials in everyway (range, speed, and load carrying ability). The B17’s used generic Allison V1710s and the B29 used a W3460 (basicly two V12’s siamesed together into one crank case). But this was late in the war, and was decided that it just wasn’t needed.
gary
Everyone pretty much so got it covered. Inlines, being narrower, present less frontal area, so less drag, so higher speed. Theoretically. Radials were far tougher though. Radials got their pilots home even with a cylinder shot off.
to further add to my post (above), is they way engine development was going and who was tooled up to build engines. In 1937 there was only one company in the inline business in North America, and Rolls Royce was the other in England (even the first ME 109’s used a Rolls Royce engine as well as all the ones sent to Spain). Rolls Royce couldn’t supply engines fast enough to meet the prewar needs of England. Let alone supply all the Allies. That’s why the War Department had Packard build engines for them. They were spitting so many Packard built Merlins that they actually had a surplus of them. I doubt that had Packard been building V12’s in 1937 you’d even know what a Wright or P&W radial was
gary
We should not forget that the radial engined fw190 were faster then the inline engined Spitfire and bf109 the entire war. And at low level the fw190 were just as fast as the legendary P-51. I think that show how sleek the radial engined fighters could be.
no they were not. By the tie the Mark IX came around the Spitfire had gained the lost ground. If your talking about a 1940 thru 1941 time frame maybe (actually the P38 was faster); then maybe. At low level flight the older Mustangs were very good if not better than most others
gary
yes it’s true the spit mk.IX were as fast as the fw190A-4 and A-5 but the germans quickly started production of the fw190A-6 that again gained the lead. Spit mk.IX were mostly unchanged throught the rest of the war but fw190 were improved and the later marks A-8/A-9 were way faster then spitfires and P-38 (not at all altitudes) I do belive that the fw190A-9 had a cruising speed that almost rivaled the flat out topspeed of the Spitfire mk.IX (I could be wrong here). It’s also true that at higher altitudes the american fighters like P-38 and p-51 were significantly faster, sometimes probably almost 70km/h faster. RAF also started to feild limited quanteties of spitfire MK. XVI that played with the D-9 and Tempest in terms of performance (inline engined btw).
My point is that radial engined fighters could be better or just as good as inline engined fighters, not if the fw190 were better or worse then the spitfire or p-51 etc.
radial engine development pretty was done by mid 1943, and about the only way they could gain power was thru larger displacements. The U.S. did this by adding more cylinder banks to the rear of the engines creating a secondary problem that haunted them all the way thru the war. Engine fires! The third and fourth row of engines tend to run hot, and then when placed in warmer climates you got a problem (look at the B29 development problems that never completely went away). I do believe that if the war in the Pacific had of lasted another 12 to 15 months we’d have been seeing W3460 powered B29’s as they were that much better than the corn cob motors (not so much that they needed the range as they had a greater bomb loading capability). In the ETO actual range wasn’t as big a problem as the PTO after mid 1944, and I’d think that if the war in Europe had have moved on into 1946 there’d have been B29’s over there just for their increase bomb loads alone.
But looking at the inline verses the radial one more time; then look at the P47D verses the P51D. The P47 had lots of power but weighed in at slightly over 10,000lb clean, and a max range of 800 miles. The Mustang configured the same way, but with 1450hp at 7,000lb. with a max range (clean) of just under a thousand miles. The Mustang was faster and more nimble than the P47D (not taking anything away from a great plane). But forget those two airframes (really compairing apples to oranges), and look at the FW’s. An A8 clean was good for about 408 mph, where as a D9 was good for 437 mph at a much greater altitude (I think the service ceiling was rated at 41K feet). Then you throw in the TA 152H factor (still similar designs although much different), and you got an altogether different ball game. It’s pretty much understood that the zenith of piston engined fighters in the ETO was the TA-152H (refering to aircraft that actually saw service). Now compair that plane to an A8 or an A9 clean. No contest!
But one thing that most everybody dosn’t know about inline engine development in the United States is that there was no serious engine programs after 1943. Packard was just spitting out a few different versions of the Merlin faster than anybody could use them! Allison stopped all engine developement programs in early to mid 1943 to concentrate of jet engine development. Rolls Royce was moving into the Griffon series as well as the next one after that, But the handwriting was on the wall by the spring of 1944. The radial was dead.
gary
Didn’t know all that squeakie, memorising it right now.
But the D-9 still had the configuration of a radial engined aircraft [:-^]